JPH03142041A - Method for continuously producing complex hollow cast billet - Google Patents

Abstract

PURPOSE:To continuously produce a complex hollow cast billet having stable quality by inserting a hollow core material preheated at temp. of m.p. or leas into a mold, pouring molten metal around the core material, packing cold material into hollow part of the core material at the time of making the outer surface of core material in melting condition, and drawing out. CONSTITUTION:The hollow core material 5 is preheated to the temp. having m.p. thereof or less with a bearing device 4 and continuously inserted in the mold 2 directly connected with a tundish 1, and the molten metal 3 is poured around the core material 5. When the outer surface of core material 5 in the molten metal 3 comes to molten or semi-molten state with the molten metal 3, the cold material 6 is packed into the hollow part 5' in the core material 5 to solidify the molten metal 3, and the core material 5 and the solidified shell 3' are diffused, joined and drawn out. By this method, crack at the time of solidifying and insertion of the molten metal into joined interface are prevented, and the complex hollow cast billet having stable quality is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a composite hollow slab as a material for seamless clad steel pipes.

(Prior art and its problems) Generally known methods for producing clad steel include an explosion bonding method, a rolling method, an overlay welding method, and a casting method.

However, the former three methods have problems in terms of productivity and cost as methods for producing materials for seamless clad steel pipes.

On the other hand, the casting method uses molten metal to enclose composite materials of different steel types, so casting can be continuous.
There are great expectations for this as a mass production process in terms of productivity and cost reduction, and many proposals have been made.

For example, JP-A-53-25233, JP-A-53-2
The methods disclosed in JP-A No. 9229 and JP-A-54-71039 are applied technologies of horizontal continuous casting, but the leakage prevention mechanism of the core material insertion part is impossible to implement as an actual operation technology. It is.

Furthermore, in the method disclosed in Japanese Patent Publication No. 44-4903, since both the core material and the laminated material are once melted at the mating interface, the mating interface is not stable and there is a problem in securing the cladding ratio.

On the other hand, in the case of the casting method, other than the build-up welding method, the joining is carried out by the heat source of the molten metal and the pressure bonding of the mating interface due to contraction during the solidification process. Therefore, if the shrinkage rate of the molten laminated metal is large compared to the core material, joining by casting (hereinafter referred to as rAs cast joining) is possible, but on the other hand, if the shrinkage rate of the molten laminated metal is small, As cast bonding is possible.
Bonding is not possible.

Particularly in cases such as clad steel pipes, where special alloys such as stainless steel are often used for the inner surface, that is, the core material side, the casting method is less applicable. Furthermore, cracks caused by shrinkage during the solidification process, which is the biggest drawback of the casting method, are the biggest bottleneck in putting it into practical use. Furthermore, the insertion of the core material at the joint is not eliminated even in the final product (seamless steel pipe) that has undergone the subsequent pipe manufacturing process, and it becomes a problem as a fatal defect in terms of quality as a clad product.

The present invention was developed in view of the above-mentioned problems in the casting method, and prevents the cracking of the molten metal during joining and the insertion of the core material into the core, and produces clad steel pipes of stable quality. The purpose of this invention is to provide a method that can continuously produce materials for use in manufacturing.

(Means for Solving the Problems) The present inventors have conducted extensive research on the above-mentioned conventional problems.
As a result of conducting experiments, the following matters were discovered and the present invention was established.

As a measure to prevent cracking caused by solidification shrinkage of molten metal,
It is effective to gradually advance the initial solidification by slow cooling.

This also leads to bringing the core material into a molten or semi-molten state, which is a condition for As cast joining.

However, even if the progress of solidification is delayed to prevent shrinkage cracks that occur during initial solidification, cracks due to subsequent shrinkage cannot be avoided as solidification progresses.

In order to prevent this, it is necessary to change the shape (outer diameter) of the core material in accordance with the solidification and shrinkage of the molten metal.

That is, it is effective to cool and shrink the core material, which is heated and expanded by heat transfer from the molten metal.

The present invention has been made based on the above findings, and involves inserting a hollow core material into a mold that is open at both ends and directly connected to a tundish, and injecting molten metal around the core material using the tundish. A method of manufacturing composite hollow slabs by continuously solidifying in a mold and drawing them out intermittently or continuously, in which the core material to be inserted into the mold is preheated to a temperature below the melting temperature of the core material. The gist of this method is to fill the hollow portion of the core material with a cold material when the outer surface of the preheated core material becomes semi-molten or molten due to heat transfer from the injected molten metal.

By the way, the preheating temperature of the core material is determined by the size (outer diameter, inner diameter) of the core material, especially its wall thickness. However, if the preheating temperature exceeds the melting temperature of the core material, the shape of the core material cannot be maintained.

Therefore, in the present invention, the preheating temperature of the core material is set to be lower than the melting temperature.

(Example) The method of the present invention will be explained below based on FIGS. 1 to 3.

In FIG. 1, 1 is a tundish, and 2 is a mold directly connected to the downstream side of the tundish 1. The molten metal 3 supplied into the tundish 1 and the mold 2 is heated to a temperature below the melting temperature by a heating device 4. Preheated hollow core material 5 is continuously inserted.

The temperature change at the mating interface at this time will be explained based on FIGS. 1 and 3.

As mentioned above, the core material 5 is heated by the heating device 4 until its surface temperature reaches an arbitrary temperature point 2 below the melting temperature, and then inserted into the molten metal 3 (FIG. 3 Φ). And molten metal 3
The core material 5 inserted therein is heated to its melting or semi-melting temperature 0 point by heat transfer from the molten metal 3, and in this temperature range O, a solid phase-liquid phase interface is formed and diffusion bonding is performed. do.

After this, the hollow part 5 of the core material 5 is filled with the cold material 6, and the core material 5
The solidified shell 3' is cooled to promote shape change in the same direction of contraction as the solidified shell 3'.

On the other hand, the temperature O of the molten metal 3 at the mating interface with the core material 5 which has been preheated and inserted into the molten metal 3 as described above is cooled by heat transfer to the core material 5 side, and the surface temperature of the core material 5 is 0. The temperature decreases to a point corresponding to this point, and this becomes the region where initial solidification progresses.

To explain this initial solidification region using the schematic diagram in FIG. 2, in the conventional casting method, the formation of the initial solidification shell 3' progresses rapidly as shown by the broken line O in FIG. 2, but in the present invention In this method, the core material 5 is preheated, so the curve ■
As shown in , coagulation progresses gradually. That is, this is a so-called slow cooling region, and in this region, the core material 5 and the solidified shell 3' are diffusion bonded.

Thereafter, the hollow part 5'' of the core material 5 is filled with the weak rams 6, and the filling of the rams 6 promotes the shape change of the core material 5 in the direction of contraction due to cooling. In addition to this effect, if the difference between the inner and outer diameters of the core material 5, that is, the wall thickness becomes smaller, it may become difficult to maintain the inner shape or it may completely melt. also plays a role in preventing these.

Next, the results of implementing the method of the present invention will be explained together with the results of implementing the comparative method.

Both the following examples and comparative examples were manufactured using composite seamless steel pipe material (base pipe), and the billet size was 20.
The insert core material is stainless steel, and the cast molten steel is low carbon steel.

Table 1 below lists the casting conditions and results of the Examples and Comparative Examples, Table 2 shows the chemical composition of the stainless steel and low carbon steel used for the insert core material and casting molten steel, and Table 3 shows the chemical compositions of the core material and cast molten steel. The liquidus point (solidus point) temperature and shrinkage rate of steel and casting molten steel are shown in comparison.

Note that when preheating the insert core material, oxidation of the insert core material was prevented in an Ar atmosphere.

In addition, the insertion core material used is a hot-made pipe that has been machined and has an outer diameter of 100 φ and an inner diameter of 60 φ.
It was made into a cabinet.

Example 1) Average casting speed by intermittent drawing is 0.75 m/min
So, cast animal f? The injection temperature in the tundish of 1tiA was ΔT = 54°C, and the core material preheating temperature was 950°C, and the maximum temperature reached at the mating interface in the casting was 14°C.
The temperature was 20°C.

This temperature corresponds to the solid-liquid coexistence temperature range of the stainless steel insert core material, and the bonding at the mating interface of the produced billet was almost perfect.

Further, after the maximum temperature at the mating interface was reached, the hollow part of the core material was filled with steel balls. In this regard, the intended effect of the present invention was confirmed as there was no cracking at the mating interface of the manufactured billet and no insertion of the stainless steel into the low carbon steel side.

Moreover, the filled steel balls could be easily discharged after casting, and post-processing did not particularly lead to an increase in cost.

Comparative Example 1) An insert core material was manufactured at room temperature without filling the hollow part of the insert core material with a cold material. Note that the other hj construction conditions are the same as in Example 1).

The maximum temperature reached at the mating interface in the casting is 1410'C
As in Example 1), the solid-liquid coexistence region of the stainless steel of the inserted core material was reached, but it took several minutes after casting.

The bonded interface of the manufactured billet had almost the same bonding condition as in Example 1), but cracks were observed on the carbon steel side of the bonded interface, and stainless steel had penetrated into that part, a so-called °° insertion.゛ was recognized.

Comparative Example 2) The insert core material was preheated to 950''C in the same manner as in Example I), and the insert core material was manufactured without filling the hollow portion of the insert core material with the path material.

Other casting conditions were the same as in Example 1).

Although the joint interface of the produced billet was in the same bonding condition as in Example 1), it was confirmed that the insertion core material was greatly deformed, and furthermore, it was confirmed that the insertion core material itself was partially melted and missing.

(Effects of the Invention) As explained above, the method of the present invention has the biggest drawback of the casting method. This prevents cracking during solidification and insertion at the mating interface, and has a great effect on stabilizing the quality of seamless clad steel pipes as final products.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of the method of the present invention, FIG. 2 is a schematic diagram of the solidification form of molten metal in the method of the present invention, and FIG. 3 is a drawing showing an example of temperature change near the mating interface in the method of the present invention. 1 is a tundish, 2 is a mold, 3 is a molten metal, 4 is a heating device, 5 is a core material, and 6 is a cold material. Figure 1 3vA

Claims (1)

[Claims] (1) While inserting a hollow core material into a mold with both ends open, which is directly connected to a tundish, molten metal is injected around the core material by the tundish, and while the molten metal is continuously solidified in the mold, intermittent or A method of manufacturing composite hollow slabs by continuous drawing, the method comprising: preheating a core material to be inserted into a mold to a temperature below the melting temperature of the core material;
A continuous manufacturing method for composite hollow slabs characterized by filling the hollow part of the core material with a cold material when the outer surface of the preheated core material becomes semi-molten or molten due to heat transfer from the injected molten metal. .